The present invention relates to an apparatus and a method for bonding two semiconductor laser chips at narrow pitches on one submount in high accuracy. The present invention is utilized in an apparatus for bonding the two laser chips (for example, combination of a red chip and an infrared chip or the like) such as a combination laser die-bonder or the like.
One example of a conventional one-chip bonding apparatus is explained below. Conventionally, a semiconductor laser chip 4 is vacuum-sucked by using a vertically provided vacuum-suction collet 6, peeled from a wafer sheet 1, transferred to an intermediate stage 2 and passed as shown in FIGS. 1 and 2. On the intermediate stage 2, a chip profile is recognized by image processing and then, a light-emission axis is recognized. A chip position is corrected in X, Y and θ directions on the basis of this data.
After the chip position is corrected in the X, Y and θ directions on the intermediate stage 2, the chip is sucked again by using the suction collet 6 and transferred onto a submount 5 placed on a bonding stage 3. The chip is bonded onto the submount 5 as it is with an adhesive or by thermo-compression bonding.
That is, the chip position is corrected only on the intermediate stage in the above-described conventional one-chip bonding apparatus. Therefore, when the chip is passed to the submount by using the collet after the position correction on the intermediate stage and the chip is mounted on the submount, a fine shift occurs. Thus, bonding position accuracy according to a specification (±2 μm or less) could not be ensured, thereby resulting in variations in a laser direction.
A method of efficiently fabricating a semiconductor laser without variations in a light-emitting direction in a die-bonding process of a semiconductor laser is disclosed in Japanese Patent Laid-Open Publication No. 7-202347. In this method, a laser chip is energized and allowed to emit light on the intermediate stage by using a probe. A light-emission axis direction is measured by image processing and the laser chip position is corrected on the basis of the measured value. When the light-emission axis direction is within a certain error range, the laser chip is sucked and transferred by a laser chip feed mechanism for die-bonding. Thus, the chip position accuracy is improved.
When a two-chip semiconductor laser device is fabricated, two kinds of light-emitting chips having different wavelengths are bonded on one submount with favorable accuracy. The chips 12, 13 are bonded one by one in FIG. 3A. When the second chip 13 is bonded, heat is applied to the first already bonded chip 12 at its junction and the clip 12 comes off. Therefore, the two chips need to be bonded at the same time.
In FIG. 3B, two conventional collets are simply arranged in a mirror image to constitute a two-chip bonding by using the one-chip bonding apparatus in FIG. 2 so that two laser chips are die-bonded on a submount.
Since a specification for a distance between light-emission points is 100±2 μm in the two-chip semiconductor laser device, the chips need to be bonded so that a distance between the respective light-emission points 14, 15 of the two laser chips 12, 13 is 100±2 μm as shown in FIG. 4. It is shown, however, that, since the collets are vertically disposed in a constitution shown in FIG. 3B, the collets interfere with each other and thereby the two chips cannot be bonded closely.
In the method disclosed in Japanese Patent Laid-open Publication No. 7-202347 as well, it is shown that, since the collets are vertically disposed, the collets interfere with each other and thereby the two chips cannot be bonded closely.
To prevent the collets from interfering with each other in the constitution where the collets are vertically disposed, a diameter of the main body of a collet might be made thinner than the chip profile. However, currently the diameter of the main body of the collet cannot be made thinner than the chip profile because a vacuum hole for vacuum-sucking a chip needs to be provided, rigidity larger than a certain level is required due to a load applied upon chip suction and chip bonding and the collet needs to be shaped so that position accuracy in attachment/replacement of the collet can be easily ensured.
As described above, when the above conventional devices are simply arranged laterally in a mirror image when a semiconductor laser device in which two laser chips are die-bonded on a submount is fabricated, there are disadvantages described below.    (1) Since the position is corrected only on the intermediate stage, a fine shift occurs after the correction on the intermediate stage when the chip is passed by using a collet or the chip is placed on the submount.    (2) The specification required distance (x in FIG. 4) between the light-emission points of the two chips is as narrow as 100 μm. Therefore, when the two chips are bonded at the same time, the normal vertical collets interfere with each other and thereby the two chips cannot be bonded at desired positions at the same time even if the light-emission point is positioned as closely to an end of the chip as possible.